Preparation of phosphorous acid esters



` Oct. l0, 1939. T. H. ROGERS E1- Al.

PREPARATION 0F PHOSPHOROUS ACID ESTERS Filed Dec. v2l, 1936 Parenfedocf. 1o, 1939 UNIT-ED STATES PREPARATION OF PHOSPHOROUS ACID ESTERS poration of Indiana Application December 21, 1936, Serial No. 117,102

18 Claims.

This invention relates to improvements in the method of preparing esters of phosphorous acid and, in particular, the alkyl phosphites.

It is knownthat alkyl phosphites can be prepared by reacting an alcohol or alcoholate with phosphorous trichloride with or without the addition of an organic base'such as pyridine. Alkyl phosphites prepared by simply treating alcohols with PG13 are mixtures of mono, di and/or tri alkyl phosphites;` and to obtain substantially pure tri alkyl phosphites or mixtures of di and tri alkyl phosphites requires careful fractionation and purification of the mixture of alkyl phosphites. i

It is-an object of the present invention to provide an expedient method of preparing substantially pure tri alkyl phosphite or substantially pure tri alkyl phosphite containing desired amounts of the di-alkyl phosphite.

Itis another object of this invention to provide a method of preparingr alkyl phosphites in whichthe formation of mono and di alkyl phosphite is avoided. 1

It is a further object of this invention to provide a method of obtaining substantially pure tri alkyl phosphite without the necessity of careful fractionation.

lOther objects and advantages of this invention will become apparent from the following description thereof', read inv conjunction with the accompanying drawing which is a schematic flow diagram-of a preferred embodiment of this invention and which forms a part of this specification.

Referring to the drawing, alcohol from a storage tank I and dimethyl aniline, from a storage tank 2 are introduced through lines 3, 4 and 5 by means of a pump 6 into one. or more glasslined reactors 1 and 8 by means of branched valved lines 9 and I0. The glass-lined reactors l and 8 are equipped with suitable agitating means such as paddle stirrers II andl I2 operated by suitable means such as motors I3 and I4.

The mixture of alcohol and dimethyl aniline is diluted with a suitable solvent, preferablyaisolvent which may be used both as a diluent and as a refrigerant such Kas methyl chloride, methyl ether, or liquefied normally gaseous hydrocarbons, such as propane, butane, pentane and/or mixtures thereof from a storage tank I and introduced into the alcohol and dimethyl aniline mixture through a valved line IS. Phosphorous trichloride from a storage tank I1 is introduced through valved lines IB'and I9 and pump 2l! into the reactors 1 and 3 through the branched valved (Cl. 26o-461) drocarbon is vaporized and the temperature reduced to the desired degree. The vaporized hydrocarbons are removed through lines 25, 25 and 21 into a trap 28 wherein entrained products from the reactors are separated from the gaseous hydrocarbons and removed through a valved line 29. Lines 25, 2B and 21 and trap 28 should be of acid resistant material. During the course of the reaction additional butane vis added to replace that which has evaporated. The reaction mixture. is allowed to stand several hours after al1 the PCla has been added.

The reaction products are removed from reactors 1 and 8 through valved lines 30, 3|, 32, a- .pump 34 and a line 35 and introduced into a separating device, such as a rotary filter, a centrifuge or filter pr'ess 36 wherein the desired alkyl phosphite is separated as filtrate from the dimethyl aniline hydrochloride formed in the reaction. The filter cake may' be washed with a suitable solvent, preferably a liquefied normally gaseous hydrocarbon, which is introduced into the filter from the hydrocarbon storage tank I5 through a line 31. The dimethyl aniline hydrochloride after being freed of the solvent by suitable means, is removed from the filter press 36 by suitable means suchvas a screw conveyor 38 and introduced through a suitable transfer means 39 into an agitator 40 wherein the dimethyl aniline is recovered as hereinafter described.

The filtrate from the ltervpress 36 is' introduced through a line 4I land a valved line 42 into one or more glass-lined, steam jacketed evaporators 43 and 44 wherein the solvent, such as the liquefied normally gaseous hydrocarbons, is

removed from the alkyl phosphite by heating in the evaporators 43 and 44 and removing the vaporized hydrocarbon through lines 45 and 46. After the solvent has been removed, the pressure Within evaporators 43 and 44 is reduced and any dimethyl aniline base, and the former withdrawn The substantially pure alkyl phosphite is removed from the evaporators 43 and through valved lines 50 and 5I by means of pumps 52 and 53, cooled in a cooler 5l and passed through a suitable filtering medium such as a canvas filter 55 and introduced into a storage tank 56. If desired, the evaporator 44 may be bypassed through a valved line 51 directly to the line 5I and thence to the storage tank 56.

'I'he pressure on the system is preferably reduced by means of asteam ejector system (not shown) on the gaseous hydrocarbon exhaust lines 58 and 58a. In order to obtain the necessary reductionin pressure, particularly the necessary vdistillation pressure which should be about 30-50 mm. of Hg., it is advantageous to use three or more steam ejectors inV series.

The gaseous hydrocarbon removed-from the trap 28, the filter press 36 and the evaporators 83 and 44 through lines 36a, 45 and 46 respectively, is combined through the valved lines 58, 58a and 58 and introduced into compressor 60 wherein the gaseous hydrocarbon is liquefied and passed through a condenser 6I and a valved line 62 to storage tank I5.

The dimethyl aniline hydrochloride introduced into theagitator Ml, as hereinbefore described, is mixed with a small amount of water, introduced through a line 63, by means of stirrer 64. 'I'he mixture of dimethyl anilinehydrochloride and water is then treated with caustic introduced into the agitator 48 from a tank 65 through a pump 68 and a line 61. The addition of caustic soda to the mixture of dimethyl aniline hydrochloride and water results in Athe formation of dimethyl methyl aniline base then introduced through avalved line 18 into a settler 1I wherein the remaining aqueous solution is separated from the from the settler 1-I through a valved line .12. The substantially pure dimethyl aniline is removed from the settler 1| by means of a pump 13, introduced through a-line 14A into a drying tower 15 from whence it passes through a line 18 to the dimethyl aniline storage tank 2. The recovered dimethyl aniline may be distilled if desired.

The method of vpracticing this invention will be illustrated by describing the method of preparing tri normal butyl phosphite, it being understood that the same is not a limitation of the invention but merely illustrative of a preferred embodiment thereof. Y f

Equal molecular volumes ofnormal butyl alcohol and dimethyl aniline from their respective storage tanks I and 2 are mixed with several volumes of liquefied butane from the butane storage tank I5, and introduced into either or'both of the glass-lined reactors 1 and 8. When the mixture of normal butyl-alcohol and dimethyl aniline in butane solution reaches a temperature of about phosphorous trichloride from the PCI: storage tank I1 in the ratio of lrmol of phosphorous trichloride to" 3 mols of i normal butyl'alcohol is introduced i'nto the reactors 1 and 8.

In the reaction between the PCL, n-butyl alcohol and dimethyl aniline, the 'dimethyl aniline hydrochloride', 4which is formed, separates on the sides of the reactors thereby preventing efficient and effective cooling by indirect means such as brine cooling. We obtain effective and efficient cooling and temperature control by direct cooling of the reaction mass by reducing the pressure within the reactors 1 and 8 whereby a portion of the butane is vaporized and the desired refrigeration thereby obtained and thereafter maintaining said pressureI constant throughout the reaction period. The vaporized butane is removed from,

the reactors through the lines 25 Vand 26 and passed into the trap 28l wherein entrained material is separated out. During the course of the reaction additional butane is added to replace that which has been evaporated. By this procedure a temperature of about 25 F. is maintained in the reactors 1 and 8 during the reaction period.

The pressure within the reactors 1 and 8 may be regulated by means of 'compressors or other suitable means such as by means of a steam ejector (as hereinbefore described). VDuring the period in which the phosphorous trichloride is added the contents of the reactors 1 and 48 are vigorously agitated by means of the stirrers II and I2. l

After the required amount of phosphorous trichloride has been added the reaction mixture is allowed to stand for a period of about 8 hours or longer during which time the temperature is maintained at about 25 F. At the end of this period the reaction mixture is introduced into the filter press 36. The reaction mixture from the reactors 1 and 8 comprises substantially pure tri normal butyl phosphite with perhaps some unreacted alcohol and/or dimethyl aniline and dimethyl aniline hydrochloride, thelatter being present in the form of a precipitate orsludge. The tri-n-butyl phosphite recovered from the filter press 36 as a filtrate should be recycled through the press until a clear product is obtained.

The dimethyl aniline chloride remaining in the filter press 36v as a filter 'cake is washed with liquefied butane, obtained from the butane storage tank I5, until'the cake is freed of occluded tributyl phosphite. The filter cake is then preferably freed of butane by suitable means, such as by heat supplied by steam coils (not shown) in the filter press 36, and removed from the filter press 36 by means of the worm or screw conveyor 38 and introduced through-transfer means 38 into the agitator I8 where it is treated to recover the-dimethyl aniline as hereinafter described.

The filtrate from the filter press 36 comprising a solution of substantially 'pure tri normal butyl phosphite in Aliquefied butane with some unreacted alcohol and/or dimethyl aniline is 'placed in the glass-lined steam jacketed still or evaporator 43 or M 4and the temperature is gradually increased whereby the butane is vaporized and removed through the lines I5 and 46 to be recompressed 'as hereinafter described. After substantially all of the butane has been removed the pressure is reduced to 30-50 mm. Hg or lower and the temperature in the still or evaporator raised to about 212 Fir-2504 F. by introducing steam into the jacket thereof, and any remaining normal butyl alcohol and/or unreacted dimethyl aniline removed and subsequently recovered by any suit-A able means.

The removal of butyl alcohol and/or dimethyl aniline is accomplished at low pressures since dimethyl aniline has a relatively high boiling point, and tributyl phosphite becomes unstable when distilled at 760 mm. Hg pressure. The operating procedure, therefore, is to ilash off the butane at atmospheric pressure, then increase the temperature and reduce the pressure slowly whereby butyl alcohol and/or dimethyl aniline is removed without decomposing the tributyl phosphite.

The product remaining in the evaporator or still y pression and returned to the butane storage tank I5.

The dimethyl aniline chloride in the agitator 40 is mixed with a small amount of water and then treated cautiouslywith a sodium hydroxideD solution of about 50% concentration. This treatment results in the formation of dimethyl aniline base and sodium chloride solution. The dimethyl aniline base which is insoluble in water rises to the surface and is separated from the sodium chloride solution by drawing off the latter through the valved line 68. The dimethyl aniline base, substantially freed of water or sodium chloride solution, is transferred to the settler 'H wherein further separation of water and/or sodium chloride solution takes place and the aqueous layer withdrawn from the bottom of the settler 'il through the Valved line 12. Thedimethyl aniline base is then passed through a-drying tower 15 and dried over calcium oxide or caustic soda to remove the last traces of moisture before being returned to the dimethyl aniline storage tank 2.

We prefer to use dimethyl aniline in the reaction since its immisclbility with Water and its high boiling point facilitates the recovery thereof from the dimethyl aniline hydrochloride cake.

If desired the separation of the dimethyl aniline base from the aqueous solution may bev eiTected lay-adding a solvent such as hexane to the dimethyl aniline base. After separation the water is drawn off and the dimethyl aniline hexane solution placed in a still and the hexane and traces ofA moisture removed by distillation. The dimethyl aniline is then cooled and returned to the dimethyl aniline storage tank.

Using the herein described method and procedure we have obtained a yield of 66% of butyl phosphite comprising about to 100% `tributyl phosphite and less than 15% of dibutyl phosphite. The amount of the dibutyl phosphite obtained is dependent upon the presence of moisture in the system and/or the ineicient removal of hydrochloric acid from the reacting mass. When the process is conducted in the complete absence of moisture and/or with an effective removal of hydrochloric acid substantially pure tributyl phosphite is obtained.

In the preparation of substantially pure trialkyl phosphites it is essential that the hydrogen chloride formed during the reaction'period be removed from the sphere of reaction. In addition to the method herein described the hydrogen chloride may be removed by conducting the reaction under a vacuum of from 0.1 to mm. of

Hg or by passing an inert gas such as ni'tgrogen, hydrogen, carbon dioxide through the reaction mixture.

While We prefer to use liquefied normally gaseous hydrocarbons as the diluent and reirigerent in ourprocess, other diluents or solvents may be used and other means for controlling the temperature may be .employed without departing a preferred embodiment of our 1nvent1on and 1s not a limitation oi the scope thereof, except as, defined inthe appended claims'.

We claim:

l. The method of preparing alkyl phosphites comprising mixing a saturated aliphatic alcohol with a tertiary amine, adding a liqueed volatile hydrocarbon solvent t0 said mixture and reacting said alcohol and tertiary amine solution with phosphorous trichloride at a temperature not higher than 50 F.

2. The method of preparing alkyl phosphites comprising mixing a saturated aliphatic alcohol with dimethyl aniline, adding a liquefied normally gaseous hydrocarbon to said mixture and reacting said solution with phosphorous trichloride at a temperature not higher than 50 F.

3. The-method of preparing alkyl phosphites comprising mixing a saturated aliphatic alcohol withy dimethyl aniline, adding liqueed butane to said mixture and reacting the liqueiied butane solution of alcohol and dimethyl aniline with phosphorous trichloride at a temperature not higher than 50 F. l

4. The method of preparing trinormal butyl phosphite comprising mixing normal butyll alcohol with dimethyl aniline, adding a liqueiied normally gaseous hydrocarbon to said mixture and reacting said mixture in the presence of the liquefied normally gaseous hydrocarbon with.

phosphorous trichloride not higher than 50 F.

5. The method of preparing substantially pure trinornal butyl phosphite comprising mixing normal butyl alcohol with dimethyl aniline, diluting said mixture with a liqueed normally gaseous hydrocarbon and reacting said diluted mixture with phosphorous trichloride at a temperature of about 25 F.-

6. The method of preparing substantially pure trinormal butyl phosphite comprising adding to a mixture normal butyl alcohol and dimethyl aniline a liqueed normally gaseous hydrocarbon,

. reacting said diluted mixture with phosphorous trichloride under pressure, reducing the pressure on said mixture, vaporizing a portion of the liquefied normally gaseous hydrocarbon whereby the temperature `of the reacting mass is maintained at a temperature not higher than 50 separating the resulting tri normal butyl phosphite from the dimethyl aniline hydrochloride and removing the liquefied normally gaseous hydrocarbon from the tri normal butyl phosphite.

7. The method of preparing substantially pure triV normal butyl phosphite comprising mixing normal butyl alcohol and dimethyl aniline, dilutying said mixture `with liquefied butane, maintaining said diluted mixture under pressure, reacting said diluted mixture with phosphorous trichloride, maintaining said reacting mass at a temperature of about 259 F. by reducing the pressure of `said reacting mass whereby a portion of the liqueiied butane is evaporated, separating the tri lnormal butyl phosphite-butane solution from the reacting mass and removing said butane from the tri normal butyl phosphite.

8. The method of preparing substantially pure tri normal butyl phosphite comprising introducing a mixture of normal butyl alcohol, dimethyl aniline and liqueed butane into a reaction vessel maintained under super atmospheric pressure. adding phosphorous trichloride to said reacting vessel, maintaining a temperature not higher than 25 F. in said reacting vessel by reducing the pressure inA the said reacting vessel whereby a portion of the liquefied butane 'is evaporated, introducing the tri normal butyl phosphite and the dimethyl aniline hydrochloride formed -in said reacting vessel into a illter press, separating the tri normal butyl phosphite-butane solution from the dimethyl anlline hydrochloride, washing said separated dimethyl aniline hydrochloride with liquefied butane, separating the liquefied butane from the tri normalbutyl phosphite by evaporation, and recovering said gaseous butane removed from said reacting vessel and said tri normalI butyl phosphite by compressing Iand condensing the same.

9. The method of preparing substantially pure tri normal butyl phosphite as described in claim 8 wherein equal molecular volumes of normal butyl alcohol 4and dimethyl aniline are reacted with 1 mol of phosphorous trichloride per 3 mols of normal butyl alcohol. D

10. In the method o! preparing a substantially pure tri alkyl phosphite by reacting a mixture ofa saturated aliphatic alcohol and dimethyl aniline with phosphorous trichloride the improvement which comprises conducting the reaction in the presence of a liqueiled normally gaseous hydrocarbon and maintaining the reaction mass at a substantially uniform vtemperature not higher than 50 F. by the evaporation of a portionV of the liquefied normally gaseous hydrocarbon.

11. In the preparation of substantially pure tri normal butyl phosphite by reacting a mixture of normal butyl alcohol and dimethyl aniline with phosphorous trichloride, the improvement which comprises conducting the reaction under superatmospheric prsure in the presence of liquefied butane and maintaining the reaction mass at a 'substantially uniform temperature not higher than 50 F. by regulating the spressure in the reaction vessel and evaporating a portion of the liqueiled butane.

12. An improved process of preparing substantially pure tri alkyl phosphiteswhich comprises introducing a mixture of a saturated aliphatic alcohol, dimethyl aniline and liqueed butane into a..reaction vessel maintained under super atmospheric pressure, adding phosphorous trichloride to said reaction4 vessel, maintaining the temperature of the reaction mass in said reaction vessel at a substantially uniform temperature not higher than 50 F. by regulating the pressure within the said reaction vessel, and evaporatinga portion of the liqueiled butane, introducing the products of reaction, comprising substantially tri alkyl phosphite and dimethyl aniline hydrochloridein butane solution, into a filter press, separating the tri alkyl phosphite and liquefied butane as a filtrate from the dimethyl aniline hydrochloride, washing the dimethyl aniline hydrochloride in the filter press with liquefied butane, combining said liqueiled butane wash with the tri alkyl phosphite and liqueed butane filtrate, separating the liquefied butane from the substantially pure tri alkyl phosphite by evaporation, recovering the separated butane, removing the dimethyl anlline hydrochloride `from said filter vpress and treating the dimethyl aniline hydrochloride with a caustic soda solution whereby dimethyl aniline is recovered.

13. The improvement in preparing substantially pure tri alkyl phosphite as described in claim 12 wherein the alcohol is normal butyl alcohol.

14. 'I'he method of preparing alkyl phosphites comprising mixing a saturatedl aliphatic alcohol with dimethyl aniline and reacting said mixture in the presence of an inert and readily volatile solvent with phosphorous trichloride at a temperature not higher than 50 F.

15. The method of preparing alkyl phosphites comprising mixing an alkyl alcohol with dimethyl than 50 F.

16. The'method of preparing -alkyl phosphites as described in claim 15 in which the diluent is a liquefied normally gaseous hydrocarbon.

17. The method of preparing alkyl phosphites as described in claim 15 in which the solvent is aniline hydrochloride are formed, separating said tri alkyl phosphite from said dimethyl aniline hydrochloride, and recovering dimethyl aniline from said dimethyl aniline hydrochloride.

THOMAS H. ROGERS. .i CLARENCE M. LOANE. l

BERNARD H. SHOEMAKER. 

